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 adqB3XgW 05O15fr2dygXCAFzSWqaabBeCvcOsvh/NCrsX4c30WcD/Is4D7o9ia7ztc4XJYNVMpYswp8KY4MjXwp95dSdVAok+rvNvhE9dKjhcAsUplcCwpW9XAfMECa0+KCi+hpI1w0lP87l+TRpoxFygFQglP35agBjw4+HDOKmPP3KOLT9fmz941bqQonpozKdb6HaL65mzMeyYeG37iKfd2HyCze2R3kYSyiVSqLCbrvpBSgNfKao+jTY0Nlq+1m2cY2i12GwZMFE2gwWbu7xsNfNd0aiBsyHAHrVDH2NSGuOOK4qRbhhZ3zgBNNhOJ886Dmi8k2HNfRFRCF2BNPLqXzAbREOkUrjRntA85zOMzkTRrnUV2T7yRp5DwYbGlby66ebNbDRnlsRBcrecRUHDe+umXf4CKisayOvIUmYe1a3RH2ZcTGnmSF3qi1EL5Hp7e4kGdvPCMm50ONbQAa6qlDrGpINCBI7wsxd+9DLg6KS3hwifEHVw8pvcTPGk9liklgaNkYQdSuV9BqMSRKtmyasuaKCj4ySiAkQZUfqj54qEh/l991hSjO6Mbc6TFnEg/p+imvD3hPvixRZtnek= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 6 Feb 2026, at 14:58, Zi Yan wrote: > On 6 Feb 2026, at 13:33, Zi Yan wrote: > >> Hit send too soon, sorry about that. >> >> On 6 Feb 2026, at 13:29, Zi Yan wrote: >> >>> On 6 Feb 2026, at 13:21, Mikhail Gavrilov wrote: >>> >>>> Hi, Yan >>>> >>>> On Fri, Feb 6, 2026 at 11:08=E2=80=AFPM Zi Yan wrote: >>>>> >>>>> Do you have a reproducer for this issue? >>>> >>>> Yes, I have a stress test that reliably reproduces the crash. >>>> It cycles swapon/swapoff on 8GB zram under memory pressure: >>>> https://gist.github.com/NTMan/4ed363793ebd36bd702a39283f06cee1 >> >> Got it. >> >> Merging replies from Kairui from another email: >> >> This patch is from previous discussion: >> https://lore.kernel.org/linux-mm/CABXGCsO3XcXt5GDae7d74ynC6P6G2gLw3ZrwAY= vSQ3PwP0mGXA@mail.gmail.com/ >> >> It looks odd to me too. That bug starts with vmalloc dropping >> __GFP_COMP in commit 3b8000ae185c, because with __GFP_COMP, the >> allocator does clean the ->private of tail pages on allocation with >> prep_compound_page. Without __GFP_COMP, these ->private fields are >> left as it is. >> >>>> >>>>> Last time I checked page->private usage, I find users clears ->privat= e before free a page. >>>>> I wonder which one I was missing. >>>> >>>> The issue is not about freeing - it's about allocation. >> >> I assume everyone zeros used ->private, head or tail, so PageBuddy has >> all zeroed ->private. >> >>>> When buddy allocator merges/splits pages, it uses page->private to sto= re order. >>>> When a high-order page is later allocated and split via split_page(), >>>> tail pages still have their old page->private values. >> >> No, in __free_one_page(), if a free page is merged to a higher order, >> it is deleted from free list and its ->private is zeroed. There should n= ot >> be any non zero private. >> >>>> The path is: >>>> 1. Page freed =E2=86=92 free_pages_prepare() does NOT clear page->priv= ate >> >> Right. The code assume page->private is zero for all pages, head or tail >> if it is compound. >> >>>> 2. Page goes to buddy allocator =E2=86=92 buddy uses page->private for= order >>>> 3. Page allocated as high-order =E2=86=92 post_alloc_hook() only clear= s head >>>> page's private >>>> 4. split_page() called =E2=86=92 tail pages keep stale page->private >>>> >>>>> Clearing ->private in split_page() looks like a hack instead of a fix= . >>>> >>>> I discussed this with Kairui Song earlier in the thread. We considered= : >>>> >>>> 1. Fix in post_alloc_hook() - would need to clear all pages, not just = head >>>> 2. Fix in swapfile.c - doesn't work because stale value could >>>> accidentally equal SWP_CONTINUED >>>> 3. Fix in split_page() - ensures pages are properly initialized for >>>> independent use >>>> >>>> The comment in vmalloc.c says split pages should be usable >>>> independently ("some use page->mapping, page->lru, etc."), so >>>> split_page() initializing the pages seems appropriate. >>>> >>>> But I agree post_alloc_hook() might be a cleaner place. Would you >>>> prefer a patch there instead? >> >> I think it is better to find out which code causes non zero ->private >> at page free time. > > Hi Mikhail, > > Do you mind sharing the kernel config? I am trying to reproduce it locall= y > but have no luck (Iteration 111 and going) so far. > It seems that I reproduced it locally after enabling KASAN. And page owner seems to tell that it is KASAN code causing the issue. I added the patch below to dump_page() and dump_stack() when a freeing page=E2=80=99s private is not zero. It is on top of 6.19-rc7. diff --git a/mm/page_alloc.c b/mm/page_alloc.c index cbf758e27aa2..2151c847c35d 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1402,6 +1402,10 @@ __always_inline bool free_pages_prepare(struct page = *page, #endif } for (i =3D 1; i < (1 << order); i++) { + if ((page + i)->private) { + dump_page(page + i, "non zero private"); + dump_stack(); + } if (compound) bad +=3D free_tail_page_prepare(page, page = + i); if (is_check_pages_enabled()) { Kernel dump below says the page with non zero private was allocated in kasan_save_stack() and freed in kasan_save_stack(). So fix kasan instead? ;) qemu-vm login: [ 59.753874] zram: Added device: zram0 [ 61.112878] zram0: detected capacity change from 0 to 16777216 [ 61.131201] Adding 8388604k swap on /dev/zram0. Priority:100 extents:1 = across:8388604k SS [ 71.001984] zram0: detected capacity change from 16777216 to 0 [ 71.089084] page: refcount:0 mapcount:0 mapping:0000000000000000 index:0= xffff888131a9da00 pfn:0x131a9d [ 71.090751] flags: 0x100000000000000(node=3D0|zone=3D2) [ 71.091643] raw: 0100000000000000 dead000000000100 dead000000000122 0000= 000000000000 [ 71.092913] raw: ffff888131a9da00 0000000000100000 00000000ffffffff 0000= 000000000000 [ 71.094336] page dumped because: non zero private [ 71.095000] page_owner tracks the page as allocated [ 71.095871] page last allocated via order 2, migratetype Unmovable, gfp_= mask 0x92cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY|__GFP_NOMEMALLOC), pid 8= 34, tgid 834 (rmmod), ts 71089064250, free_ts 67872485904 [ 71.099315] get_page_from_freelist+0x79b/0x3fa0 [ 71.100216] __alloc_frozen_pages_noprof+0x245/0x2160 [ 71.101177] alloc_pages_mpol+0x14c/0x360 [ 71.101704] alloc_pages_noprof+0xfa/0x320 [ 71.102497] stack_depot_save_flags+0x81c/0x8e0 [ 71.103100] kasan_save_stack+0x3f/0x50 [ 71.103624] kasan_save_track+0x17/0x60 [ 71.104168] __kasan_slab_alloc+0x63/0x80 [ 71.104694] kmem_cache_alloc_lru_noprof+0x143/0x550 [ 71.105385] __d_alloc+0x2f/0x850 [ 71.105831] d_alloc_parallel+0xcd/0xc50 [ 71.106395] __lookup_slow+0xec/0x320 [ 71.106880] lookup_slow+0x4f/0x80 [ 71.107463] lookup_noperm_positive_unlocked+0x7d/0xb0 [ 71.108173] debugfs_lookup+0x74/0xe0 [ 71.108660] debugfs_lookup_and_remove+0xa/0x70 [ 71.109363] page last free pid 808 tgid 808 stack trace: [ 71.110058] register_dummy_stack+0x6d/0xb0 [ 71.110749] init_page_owner+0x2e/0x680 [ 71.111296] page_ext_init+0x485/0x4b0 [ 71.111902] mm_core_init+0x157/0x170 [ 71.112422] CPU: 1 UID: 0 PID: 834 Comm: rmmod Not tainted 6.19.0-rc7-di= rty #201 PREEMPT(voluntary) [ 71.112427] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS = 1.17.0-debian-1.17.0-1 04/01/2014 [ 71.112431] Call Trace: [ 71.112434] [ 71.112436] dump_stack_lvl+0x4d/0x70 [ 71.112441] __free_frozen_pages+0xef3/0x1100 [ 71.112444] stack_depot_save_flags+0x4d6/0x8e0 [ 71.112447] ? __d_alloc+0x2f/0x850 [ 71.112450] kasan_save_stack+0x3f/0x50 [ 71.112454] ? kasan_save_stack+0x30/0x50 [ 71.112458] ? kasan_save_track+0x17/0x60 [ 71.112461] ? __kasan_slab_alloc+0x63/0x80 [ 71.112464] ? kmem_cache_alloc_lru_noprof+0x143/0x550 [ 71.112469] ? __d_alloc+0x2f/0x850 [ 71.112473] ? d_alloc_parallel+0xcd/0xc50 [ 71.112477] ? __lookup_slow+0xec/0x320 [ 71.112480] ? lookup_slow+0x4f/0x80 [ 71.112484] ? lookup_noperm_positive_unlocked+0x7d/0xb0 [ 71.112488] ? debugfs_lookup+0x74/0xe0 [ 71.112492] ? debugfs_lookup_and_remove+0xa/0x70 [ 71.112495] ? kmem_cache_destroy+0xbe/0x1a0 [ 71.112500] ? zs_destroy_pool+0x145/0x200 [zsmalloc] [ 71.112506] ? zram_reset_device+0x210/0x5e0 [zram] [ 71.112514] ? zram_remove.part.0.cold+0x8f/0x37f [zram] [ 71.112522] ? idr_for_each+0x10b/0x200 [ 71.112526] ? destroy_devices+0x21/0x57 [zram] [ 71.112533] ? __do_sys_delete_module+0x33f/0x500 [ 71.112537] ? do_syscall_64+0xa4/0xf80 [ 71.112541] ? entry_SYSCALL_64_after_hwframe+0x77/0x7f [ 71.112548] kasan_save_track+0x17/0x60 [ 71.112551] __kasan_slab_alloc+0x63/0x80 [ 71.112556] kmem_cache_alloc_lru_noprof+0x143/0x550 [ 71.112560] ? kernfs_put.part.0+0x14d/0x340 [ 71.112564] __d_alloc+0x2f/0x850 [ 71.112568] ? destroy_devices+0x21/0x57 [zram] [ 71.112575] ? __do_sys_delete_module+0x33f/0x500 [ 71.112579] d_alloc_parallel+0xcd/0xc50 [ 71.112583] ? __pfx_d_alloc_parallel+0x10/0x10 [ 71.112586] __lookup_slow+0xec/0x320 [ 71.112590] ? __pfx___lookup_slow+0x10/0x10 [ 71.112594] ? down_read+0x132/0x240 [ 71.112598] ? __pfx_down_read+0x10/0x10 [ 71.112601] ? __d_lookup+0x17b/0x1e0 [ 71.112605] lookup_slow+0x4f/0x80 [ 71.112610] lookup_noperm_positive_unlocked+0x7d/0xb0 [ 71.112614] debugfs_lookup+0x74/0xe0 [ 71.112618] debugfs_lookup_and_remove+0xa/0x70 [ 71.112623] kmem_cache_destroy+0xbe/0x1a0 [ 71.112626] zs_destroy_pool+0x145/0x200 [zsmalloc] [ 71.112631] ? __pfx_zram_remove_cb+0x10/0x10 [zram] [ 71.112638] zram_reset_device+0x210/0x5e0 [zram] [ 71.112645] ? __pfx_zram_remove_cb+0x10/0x10 [zram] [ 71.112651] ? __pfx_zram_remove_cb+0x10/0x10 [zram] [ 71.112658] zram_remove.part.0.cold+0x8f/0x37f [zram] [ 71.112665] ? __pfx_zram_remove_cb+0x10/0x10 [zram] [ 71.112671] idr_for_each+0x10b/0x200 [ 71.112675] ? kasan_save_track+0x25/0x60 [ 71.112678] ? __pfx_idr_for_each+0x10/0x10 [ 71.112681] ? kfree+0x16e/0x490 [ 71.112685] destroy_devices+0x21/0x57 [zram] [ 71.112692] __do_sys_delete_module+0x33f/0x500 [ 71.112696] ? __pfx___do_sys_delete_module+0x10/0x10 [ 71.112702] do_syscall_64+0xa4/0xf80 [ 71.112706] entry_SYSCALL_64_after_hwframe+0x77/0x7f Best Regards, Yan, Zi